1. Field of the Invention
The present invention relates to a solid-state image pick-up device for color image pick-up such as a CCD or a CMOS sensor, and more particularly to a solid-state image pick-up device capable of distinguishing a photographing light source type with high precision and recording a color image in an excellent white balance and an image pick-up apparatus mounting the solid-state image pick-up device.
2. Description of the Related Art
FIG. 22 is a plane view showing a conventional solid-state image pick-up device described in JP-A-10-136391, for example. The solid-state image pick-up device is referred to as a so-called honeycomb pixel arrangement having such a structure that a photodiode including a large number of green (G) color filters is provided at a predetermined interval vertically and horizontally and photodiodes having blue (B) and red (R) color filters are alternately provided in positions shifted by a ½ pitch from each photodiode in each row and each column. In an example shown in the drawing, octagonal frames represented as “R”, “G” and “B” indicate red, green and blue color filters respectively, and corresponding photodiodes are provided on the underside thereof (the underside of a paper). More accurately, the octagonal frame represents the shape of the photodiode, and the red, green and blue color filters are provided in larger sizes than the sizes of the octagonal frames (for example, an octagon or a square).
A light is incident through each color filter so that a signal charge stored in each photodiode is read onto a vertical transfer path 20 formed on the side of each photodiode as shown in an arrow a. The signal charge is transferred along the vertical transfer path 20 as shown in an arrow b to reach a horizontal transfer path 21. Subsequently, the signal charge is transferred along the horizontal transfer path 21 as shown in an arrow c and is read from the solid-state image pick-up device. An amount of the signal charge read from each pixel (photodiode) has a value corresponding to an amount of a light received by each photodiode.
Thus, the color filter is superposed on the surface of each photodiode of the solid-state image pick-up device. The color filter is manufactured by using pigments or dyes, for example. FIG. 23 shows the spectral sensitivity of a digital camera using a solid-state image pick-up device provided with a conventional each color filter in which the color filters R, G and B transmit lights having wavelengths corresponding to red, green and blue colors and cut lights having other wavelengths. For example, the conventional red color filter R is manufactured to transmit a light having a wavelength of 580 nm or more and to uniformly cut lights having lower wavelengths as shown in FIG. 23.
In the case in which various scenes are to be photographed by means of an image pick-up apparatus such as a digital still camera or a digital video camera which mounts a solid-state image pick-up device, the photographing is carried out under various illuminating light sources. For this reason, it is preferable that the image pick-up apparatus should automatically regulate the gains of R, G and B signals to adjust a white balance also in the photographing under any light source. However, the image pick-up apparatus is to detect a photographing light source type with high precision in order to adjust the white balance irrespective of the photographing light source type.
For this reason, conventionally, a color temperature detecting circuit is mounted on the image pick-up apparatus and one image photographed by the solid-state image pick-up device is divided into 8×8=64 regions, for example, and a set of data of ΣR/ΣG and data of ΣB/ΣG in each divided region are thus obtained, and these 64 sets of data are plotted into a two-dimensional space extended over an R/G axis and a B/G axis and a photographing light source type is detected based on the shape of the distribution (ΣR, ΣG and ΣB represent the sum of respective color signals).
According to the color temperature detecting circuit in accordance with the conventional art, it is possible to roughly distinguish the photographing light source type. However, there is a problem in that it is hard to distinguish a leaf green color under a dark sunlight from a white color under an ordinary type white fluorescent lamp (an F6 light source) or a 3-wavelength type fluorescent lamp, for example.
In order to automatically regulate the white balance very finely by using the image pick-up apparatus, it is necessary to distinguish a sunlight from a fluorescent lamp with high precision and to distinguish different kinds of fluorescent lamps with high precision (for example, to distinguish an ordinary type white fluorescent lamp, a 3-wavelength type daylight color fluorescent lamp, a 3-wavelength type day white fluorescent lamp and a 3-wavelength type bulb color fluorescent lamp). It has been desired to develop a technology for implementing the distinction of these photographing light source types with high precision at a low cost.
Further, in a digital camera mounting such a solid-state image pick-up device, it is effective that the spectral sensitivity of the green color is broadened toward the long wavelength side, and furthermore, the spectral sensitivity of the red color is broadened toward the short wavelength side as in characteristic lines G′ and R′ shown in broken lines of FIG. 23 in order to enhance the sensitivity of the solid-state image pick-up device.
As described above, it is effective that the spectral sensitivities of R and G are broadened in order to enhance the sensitivity of the solid-state image pick-up device. On the other hand, however, there is a problem in that the spectral sensitivities of R and G are broadened, resulting in dirty colors and a reduction in the reproducibility of the colors.
In the case in which the image of a human flesh color is picked up under an F6 light source (an ordinary type white fluorescent lamp), particularly, the flesh color becomes close to yellowish green (YG) if the spectral sensitivity of G is broadened toward the long wavelength side, which is not preferable. This is mainly caused by the fact that a radiant energy generated from the F6 light source is biased toward the vicinity of 580 nm as shown in FIG. 2. When the spectral sensitivity of G is broadened to reach the wavelength region, the flesh color is greatly close to YG. Also in an F12 light source (3-wavelength type bulb color fluorescent lamp), moreover, the flesh color is closer to YG if the sensitivity of G reaches a radiation peak (approximately 610 nm) more greatly in a red light region.
More specifically, if the spectral sensitivity of G is broadened toward the long wavelength side in such a manner that a sensitivity at 600 nm is “10” or more when the peak sensitivity of G is set to be “100”, the flesh color is closer to YG. If the spectral sensitivity of R is broadened toward the short wavelength side in such a manner that the sensitivity of R at 575 nm is “10” or more when the peak sensitivity of R is set to be “100”, the flesh color is close to YG under the F6 light source.
For this reason, the conventional digital camera has a problem in that the spectral sensitivities of R and G cannot be greatly broadened and the sensitivity of the digital camera cannot be enhanced.